The invention relates to anionic polymerization catalyst compositions useful for preparing homopolymers and copolymers of conjugated dienes having a high 1,4-trans-dienyl content, and more particularly polymers of 1,3-butadiene having a high 1,4-trans-butadienyl content.
Homopolymers of 1,3-butadiene and especially block copolymers of 1,3-butadiene with vinylaromatic compounds or with other conjugated diene compounds, the polymers having a high 1,4-trans-butadienyl content and a low vinyl content, are receiving a lot of attention. Such polymeric materials are claimed to have a number of improved performance characteristics such as high green strength, increased wear resistance and improved processability, when compared with corresponding polymers having a low 1,4-trans-butadienyl content. The 1,3-butadiene polymers having a high 1,4-trans-butadienyl content may conveniently be prepared via the anionic polymerization of 1,3-butadiene as such or in combination with other suitable monomers.
Methods for the preparation of such high 1,4-trans-butadienyl polymers are known and have been described in e.g. U.S. Pat. No. 4,080,492, in which process a catalyst composition is employed consisting of (a) an organolithium compound and (b) a cocatalyst system consisting of a compound of barium or strontium and an organometallic compound of aluminum or zinc. When comparing the anionic polymerization process according to this patent with the organolithium-initiated anionic polymerization of 1,3-butadiene, it could be observed that the catalyst composition employed in the process for the preparation of the high 1,4-trans-butadienyl polymer had a lower activity, i.e. the polymerization reaction proceeded more slowly. The lower activity of the catalyst composition appears to be the price for obtaining a high 1,4-trans-butadienyl content in the 1,3-butadiene polymer.
Generally, the use of a less active catalytic system will not pose a serious problem. However, with the preparation of certain types of 1,3-butadiene copolymers having a high 1,4-trans-butadienyl content, such as the corresponding 1,3-butadiene block copolymers, the use of less active catalyst compositions could be a serious disadvantage. In the preparation of such block copolymers, it is very important to achieve substantially complete monomer conversion for each polymer block before the addition of the monomer or monomer mixture required for preparation of subsequent blocks. The use of a less active catalyst composition could seriously delay the addition of the monomer required for the subsequent polymer block, or otherwise could result in the formation of a non-desired intermediate copolymer block.
It will therefore be appreciated that with certain polymerization process modes, the effects of using a less active catalyst system may be disadvantageous if not unacceptable. Hence there is considerable need for improvement in the activity of catalyst compositions which are used in the preparation of conjugated diene polymers, such as 1,3-butadiene polymers, having a high 1,4-trans-dienyl content.
The problem underlying the present invention is developing a high activity catalyst compositions for preparing conjugated diene polymers, particularly 1,3-butadiene polymers, having a high 1,4-trans-dienyl content.